Index properties soil, engineering properties of soil,

 Index properties of soil 

These are those properties which are used to identify and classify the soil.

Example- water content, specific gravity, unit weight of the soil, particles size distribution, consistency limits, sensitivity, toughness, activity, etc.

Engineering properties 

Properties which govern the strength of the soil.

Example- Cohesion, shear strength ,Bearing capacity..

Index properties 

(1)- Water content .

It is defined as the ratio of weight of water to weight of solid .

w= [Ww/Ws]

Range of water content w≥0.

Determination of water content 

There are  seven method to determine water content .

(1)- Oven drying method 

(2)- Sand bath method.

(3)- Alcohol method 

(4)- Radiation method.

(5)- Pycnometer method .

(6)- Torsional Balance method 

(7)- Calcium carbide method .

Note 

Out of these 7 methods oven drying method is the most accurate method .

It is a laboratory method.

(1) Oven drying method 

Step 1 

take a empty container and weight it . We will say this weight W1 

Step 2- 

Fill empty container with moist soil and weight it .it is W2

Step 3 

Keep the soil in the temperature controlled oven for 24 hours at a temperature 105°C to 110°C

Step 4 

When the soil has dried , remove the container from the oven.

Step 5 

Find the weight of the dry soil and saying it W 3 .

Now calculate water content by using the formula .

Weight of water Ww= (W2-W3 )

Weight of solid Ws=(W3-W1)

 w= [W₂-W₃] / [W₃ -W₁]*100%

 *This method is suitable for inorganic soil 

(1) Inorganic soil 

(1) Gravel 

(2) Sand 

(3) Silt 

(4) Clay 

Note- if temperature is increase 110°C there is disintegration of Solid particles. Then the structure water comes out from particles. It gives inaccurate results.

So suitable range of temprature is  105 ° C to 110 ° C.

Organic soil 

 if soil having high organic content then temprature should not greater than 60° C. Because organic matters Oxides at 60° C.

If the soil having high gypsum content.

Then we should not increase the temperature above 80° C. To avoid loss of water of crystallization.

(2) Sand bath method 

Step 1  clean the empty container and Weight (W1).

Step 2 take required quantity of moisture soil and weight it W2 

Step 3 place the container on the sand bath and heat the sand bath.

Step 4 when drying is complete, remove the container from the sand bath ,cool and weight (W3).

     for water content 

                 w=[W2-W3/W3-W1] 

Important points ( Disadvantages)

* In this method temprature is not  controlled.

* If temperature increases above 110° C particles loss structural water .

* If soil is organic then above 60° C it will be oxides 

* If Soils have gypsum content then we should not increase the temperature above 80° C to avoid loss of water of crystallization.

So this method should not be used for organic soil .

Advantages 

1- It is field method 

2- less time required.

3- quick results 

(3) Alcohol methods.

Step 1 - 

Clean  the evaporating dish, dry and weigh (W1).

Step 2. 

 Take soil sample in dish and weigh (W2).

Step 3 

 Pour methylated spirit over the soil at the rate of about one mili litre  for every gram of soil.

Step 4 

 Place the evaporating dish on a surface ,stir the soil constantly with spatula or knife.

Step 5 

After the methylated spirit has burnt away completely allow the dish to cool and weigh (W3). 

     w=[(W2-W3)/(W3-W1)]x100 

Important points .

1-It is a field method 

2-It can't be used when soil have high gypsum content and high organic content .

(4) Radiation method 

1- in this method two casing are lowered in the ground where the moisture content is to be determined.

2- One of the casing consist of radio active material Cobalt-60 and other consist of detector. 

3-Radioactive material emitted neutron when activated.

4-these neutrons hit hydrogen atom, present in the water resulting in loss in energy of the neutron,that is detected by detector and is further calibrated to give the water content of soil. 

Important points 

(a)- It is a field method.

(b)- It is accurate method.But very expensive.

(c) In this method required skill man power.

(5)Pycnometer method 

This is quick laboratory method.

Step 1

Weighing the empty dried Pycnometer bolte with conical cap W1.

Step 2 

Take 200-400 g moist soil in the Pycnometer and weighed W2 

Step 3 

Fill the water upto the conical top ,dried outside and weighed (W3).

Step 4 

The Pycnometer is emptied, cleanned  thoroughly and weighed after filling it with water upto the top (W4). 

Water content w=[(W2-W1)/(W3-W4)(Gs-1/Gs)-1]x100.

(6) Torsional Balance Moisture Meter Method.

(i)Keep the soil sample in sample pan of the infrared lamp and spread evenly.

(ii) Start the infrared lamp and keep the temperature under 110°C

(iii) The water content can be read directly from the drum scale.

(iv) When the pointer of the drum scale become stationary,it indicates the soil has dried .This reading is the water content based on the dry weight. 

Important point

In this method the soil used which is quickly absorb moisture 

1.            Water content, w = w’ / (1 – w’) 

(7) Calcium carbide method. 

1. Take the soil sample in powdered form in the container and mix it thoroughly with the calcium carbide.
2. The acetylene gas produced exert pressure on the diaphragm.
3. The dial gauge is so calibrated that it gives the water content of soil directly based on the total mass (wt)..  

H2O+CaC2→C2H2+CaO 

         Water content ,w = w’ / (1 – w’) 

The method is very quick - the result can be obtained in 5 to 10 minutes. The field kit contains the moisture tester , a small single pan weighing balance , a bottle containing calcium carbide and a brush. A big container permits the use of 26 g sample. In order that balls, having wet soil inside and dry soil outside, may not form during the reaction with calcium carbide, the soil may be mixed with perfectly dry sand. In the larger container, two 30 mm diameter balls are placed for proper pulversation of clay soils, This method is specifically suited to a circumference where the water content is to be quickly determined for purpose of proper field control , such as in the compaction of an embankment.

Also see .. 

Specific gravity of soil.....